$*)X:H_2NR(COOH)_n:x mol$$\begin{cases}x(R+16+45n)=14,7 (1) \\x(R+16+67n)=19,1 (2)\\x(R+52,5+45n)=18,35 (3) \end{cases}$
$*)\begin{cases}(2)-(1) \\ (3)-(1) \end{cases}\Rightarrow \begin{cases}xn=0,2 \\x=0,1 \end{cases}\Rightarrow n=2\Rightarrow R=41\Rightarrow R:C_3H_5$
$\Rightarrow X:H_2NC_3H_5(COOH)_2$
$\Rightarrow X:HOOC-CH(NH_2)-CH_2-CH_2-COOH$
$HOOC-CH_2-CH(NH_2)-CH_2-COOH$
$.................................................$